Remove GraphQL mutation to create an Abuse Report Note

What does this MR do and why?

This change removes the ability to create new abuse report notes through the GraphQL API. This feature is related to the abuse_report_notes feature flag which has never been released and has been approved for removal in this breaking change issue: gitlab-com/Product#14362

References

• !209207 (merged)
• !165931 (merged)
• !209042
• #553432
• gitlab-com/Product#14362

Screenshots or screen recordings

This feature was never released.

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